(a) Technical Field
The present invention relates to a liquid crystal display (LCD) device.
(b) Related Art
In general, liquid crystal display (LCD) devices include two display panels having pixel electrodes and a common electrode, and a liquid crystal layer having an anisotropy dielectric disposed between the display panels. The pixel electrodes are arranged in a matrix, and are connected to switching elements such as thin film transistors (TFTs) to sequentially receive data voltages by rows. The common electrode is formed on the entire surface of one of the display panels and may receive a common voltage. A liquid crystal capacitor is formed with the pixel electrode, the common electrode, and the liquid crystal layer therebetween. The liquid crystal capacitor and the switching element connected to the liquid crystal capacitor form a pixel unit.
In LCD devices, a voltage is applied to the two electrodes to form an electric field on the liquid crystal layer. A desired image is obtained by controlling the strength of the electric field and controlling the transmittance of light passing through the liquid crystal layer. When an electric field is applied to the liquid crystal layer in one direction, degradation of the LCD device may occur. In order to prevent such degradation, the polarity of the data voltage with respect to a common voltage may be inverted for each frame, row, or pixel.
Because of the slow response rate of liquid crystal molecules, it takes time to charge a liquid crystal capacitor up to a target voltage (hereinafter, “pixel voltage”) to obtain a desired luminance. This time depends on the difference between the target voltage and the voltage previously charged to the liquid crystal capacitor. Thus, when the difference between a target voltage and the previous voltage is great and the target voltage is applied at a beginning stage, it may be impossible to reach the target voltage during the time a switching element is turned on.
Accordingly, a dynamic capacitance compensation (DCC) method has been developed. When the voltage applied between both ends of a liquid crystal capacitor is greater, charging time is reduced. The DCC method raises the data voltage to be applied to each pixel to a voltage greater than a target voltage. This shortens the time required for the pixel voltage to reach the target voltage. The data voltage is practically the difference between a data voltage and a common voltage, but the DCC method sets the common voltage to 0V for the sake of convenience.
The DCC method however, requires a frame memory and a driving circuit for performing DCC computations. As a result, the DCC method requires changes in circuit design and raises manufacturing costs.
Small LCD devices such as those used for mobile phones, perform row inversion that inverts the polarity of the data voltage with respect to the common voltage by rows to reduce power consumption. Because small LCD devices can require high resolutions, power consumption is an important factor in such devices. In particular, power consumption will be increased in the performance of DCC computation because the DCC method requires additional computations or circuits.
Further, the data voltage range used for displaying an image in the case of row inversion is smaller than that for dot inversion in which the polarity of a data voltage with respect to the common voltage is inverted by pixels. Thus, if the threshold voltage for driving liquid crystals is high, such as in a vertical alignment (VA) mode liquid crystal display, the data voltage range for gray representation used for actual image display becomes as low as the threshold voltage. Thus, luminance representation in such configurations is difficult.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.